This invention relates to a multi-cylinder combustion structure for an oil burner, and more particularly to a multi-cylinder combustion structure for an oil burner which is adapted to be red-heated to outward emit heat-rays for heating a room or space.
An oil burner of the combustion cylinder structure type which is adapted to heat a room or space by means of heat rays emitted from a combustion cylinder structure red heated by combustion of fuel oil therein is so constructed that the combustion cylinder structure is directly observed, unlike an oil burner of the hot air discharge type which is adapted to heat a room or space by means of hot air discharged from the oil burner; thus, it is required to satisfactorily exhibit an aesthetic effect as well as a heat emission function. For an oil burner of the combustion cylinder structure type, there has been widely used a multi-cylinder combustion structure which includes inner and outer cylindrical members concentrically arranged so as to be spaced from each other at a suitable distance and red-heated by combustion of fuel oil therein and a heat-permeable cylinder arranged outside the outer cylindrical member so as to permit heat rays emitted from the red-heated inner and outer cylindrical members to be outward discharged therethrough for heating a space. The so-constructed multi-cylinder combustion structure was improved so as to carry out complete combustion of fuel oil, even when a wick is lowered to reduce the amount of combustion to a degree sufficient to cause the upper end of a combustion flame formed by combustion of fuel oil to be positioned in a gap between the inner cylindrical member and the outer cylindrical member. This is accomplished by arranging a central cylinder inside the inner cylindrical member. Unfortunately, the multi-cylinder combustion structure fails to keep the cylindrical members, particularly, the outer cylindrical member satisfactorily red-heated when the wick is thus lowered to cause the upper end of a combustion flame to be positioned in the gap between both cylindrical members, because the portion of the outer cylindrical member which the combustion flame does not reach is observed to be dark and the dark portion is positionally irregular in the circumferential direction of the outer cylindrical member. Such phenomenon causes a user often to misunderstand that the structure carries out incomplete combustion, although complete combustion actually takes place in the structure.
A combustion cylinder construction which has been conventionally used for an oil-fired cooking stove is constructed so as to be accommodated to a wide variation in combustion. More specifically, it is generally constructed in such a manner that a central cylinder is arranged inside an inner cylindrical member to separate the flow of air directed to the lower portion of the inner cylindrical member from that directed to the upper portion thereof, resulting in air in a gap between the inner cylindrical member and the central cylinder being controlled so as to be fed via small through-holes of the inner cylindrical member to a gap between the inner cylindrical member and an outer cylindrical member. Such construction permits complete combustion to be accomplished even when the upper end of a combustion flame is positioned in the gap between the outer cylindrical member and the inner cylindrical member to to reduce the amount of combustion.
Such construction is utilized for the above-described multi-cylinder combustion structure for heating a space or room, to thereby permit complete combustion to be attained even when the amount of combustion is kept at a decreased level.
More particularly, in the multi-cylinder combustion structure free of such a central cylinder as described above, when the combustion operation is carried out while positioning the upper end of a combustion flame in the gap between the inner cylindrical member and the outer cylindrical member to keep combustion reduced, fuel oil of a high molecular weight vaporized from a wick is thermally decomposed into combustible gas of low molecular weights by combustion heat at a portion of the gap in which the combustion flame exists, to thereby cause the volume of gas at the portion being increased; whereas such decomposition does not substantially take place at a portion of the gap above the combustion flame. This results in a draft being produced in the gap to cause air in the inner cylindrical member to tend to be introduced via the through-holes of the inner cylindrical member into the portion of the gap above the combustion flame and upward flow, to thereby fail to feed a sufficient or effective amount of air to the combustion flame, leading to incomplete combustion.
On the contrary, in the multi-cylinder combustion structure having a central cylinder arranged inside the inner cylindrical member, the upper portion of the gap between the inner cylindrical member and the outer cylindrical member is fed with air flowing from the interior of the central cylinder to the upper portion of the inner cylindrical member; whereas a combustion flame formed when the wick is lowered to reduce the amount of combustion is fed with air introduced to the gap between the central cylinder and the inner cylindrical member, thus, the combustion flame is fed with air in an amount sufficient to carry out complete combustion irrespective of air flowing above the combustion flame. This ensures complete combustion of the flame even when the combustion operation is carried out while keeping the amount of combustion reduced. Thus, it will be noted that the combustion performance of the multi-cylinder combustion structure including the central cylinder is substantially affected by control of air in the gap between the central cylinder and the inner cylindrical member.
For this purpose, it has been conventionally proposed to incorporate a control member in the combustion structure. For example, Japanese Utility Model Publication No. 73/1955 discloses arrangement of such a control member at each of the upper and lower ends of the central cylinder. Japanese Utility Model Publication No. 3577/1955 discloses arrangement of the control member at the central portion of the central cylinder. Japanese Utility Model Publication No. 32174/1972 discloses mounting of the control member at the lower end of the central cylinder. Finally, Japanese Utility Model Publication No. 35707/1972 discloses arrangement of the control member at the upper end of the central cylinder.
For the same purpose, it is proposed that the central cylinder is provided with small through-holes. For example, the assignee has proposed that the central cylinder be formed at only the lower portion thereof with small through-holes, as disclosed in Japanese Utility Model Publication No. 24347/1979.
In the multi-cylinder combustion structure for outward discharging heat rays from the red-heated inner and outer cylindrical members through the heat-permeable cylinder for heating a room or space, the inner and outer cylindrical members are red-heated by a combustion flame produced therein and combustion gas produced by combustion and heated to a high temperature by heat of the combustion. Unfortunately, the conventional multi-cylinder combustion structure fails to prevent red-heating of the inner and outer cylindrical members from being positionally varied depending upon a positional variation in combustion flame and a variation in flowing of the combustion gas when the wick is lowered to decrease the amount of combustion, although it ensures complete combustion even in the decreased combustion operation as described above. In particular, the red-heated portion of each of the inner and outer cylindrical members is rendered positionally irregular or unstable in the circumferential direction of the cylindrical member. The gap defined between the inner cylindrical member and the outer cylindrical member is formed into an annular shape, so that the conventional combustion structure fails to permit the upper end of the combustion flame produced in the gap when the wick is lowered to be horizontally or circumferentially uniform all over the gap irrespective of ensuring complete combustion. For example, this often causes only one side of the cylindrical member to be red-heated and the other side to be kept dark. Thus, the conventional multi-cylinder combustion structure is obliged to be constructed so as to red-heat the whole inner and outer cylindrical members.